During the six Apollo moon landings, astronauts left American flags planted into the lunar soil. NASA's Lunar Reconnaissance Orbiter, which has surveyed the moon for the past three years, has revealed that all but one of them are still standing:

The photos from Lunar Reconaissance Orbiter (LRO) show the flags are still casting shadows - except the one planted during the Apollo 11 mission.

This matches Buzz Aldrin's account of the flag being knocked over by engine exhaust as Apollo 11 lifted off. [...]

Prof Mark Robinson, the chief scientist for the spacecraft's camera instrument, LROC, said in a blog entry: "From the LROC images it is now certain that the American flags are still standing and casting shadows at all of the sites, except Apollo 11."

The Arizona State University scientist added: "The most convincing way to see that the flags are still there, is to view a time series of LROC images taken at different times of day, and watch the shadow circle the flag."

"Personally I was a bit surprised that the flags survived the harsh ultraviolet light and temperatures of the lunar surface, but they did. What they look like is another question (badly faded?)"

At the link, you can see a satellite image of one of those flag shadows.